pipe question

[Kham]

i remember a discussion about after market pipe in a car. if you run the pipe straight, means you gut the catalyst, you lose some back pressure which means the car suffers low end torqu. for a turbo model, this is not a big deal because the turbo will spool up quick enough to make up the lost.

my question is this true for motorcycle espacially the 600 as they have low enough mid range torqu?

[JJ]

I remember a story about racing (cars) and they enforced a muffler rule. All the engine builders were bitching about it untill they found out they could make more hp with a little back pressure. IMO that is why Harley's have alot of engine problems becasue they run drag pipes with no back pressure and burn the motors up. Now if your making top fuel hp 7-8000 then I would have to say that back pressure would hurt but you also notice they rebuild every run. You should make this a poll I guess. I vote for back pressure here.

[Kham]

im wondering if most people also upgrade the fuel management when they changing out the pipe for either more gain at high end or just compensate for a lost at low end. if not is it an automatic gain? just throwing this out.

[JJ]

Keep in mind bigger isn't always better. To large of an injector or carb can hurt performance just as to big of an exhaust can do the same. But to small of the above can also rob performance. So your best bet is to find out what size pipe, fuel, etc to run for the hp you are capable of making. I think most people run open exhaust becasue they think it sounds cool and they aren't really worried about overall performance. If it sounds like it will run 10's more than likely it won't..... just watch Fast and Furiuos .

[snowborder]

Calling TLRMAN please bless us with an explanation before we theorize ourselves into stock setups.

[Kham]

[Green Hornet]

Back pressure is needed, but it depends on the appication.

It depends on what kind of power curve you're looking for. For a comprimise like on the street, back pressure is good because you don't loose out on the low end, mids or the top end.

This is why high end pipes like Arrow or Akrapovic are tuned to specific motorcycles to max out the entire power band, which in turns end up making the bike faster then a straight thru design like D&D.

[TLRMan]

Originally posted by snowborder
Calling TLRMAN please bless us with an explanation before we theorize ourselves into stock setups.

Ha! Now you've done it....
Lets start with "Forced Induction"
If you are using a blower or Turbo, you don't need back pressure..
You don't need the reversion, or reverse pulse of the exhaust wave to "push" some of the lost air/fuel charge back into the cylinder ...Does the term over scavange sound familiar?
You get a very fresh air/fuel charge with forced induction, and no leftover exhaust gasses present.

For "naturally aspirated" applications, it's nice to have some..for the reasons I stated above. Some of the fresh air/fuel, makes it out of the cylinder, during the exhaust and intake valve overlap event. At lower RPM's the cams allow the valves to flow more than the engine requires so back pressure helps. Seems like everyone is using the EXUP concept these days because it works...

Once the rpm's get to where the cams come in, you don't need it as much...On 2 cycle applications, the "Tuned Pipe" or expansion chamber does return a pulse back to the engine, and supercharges it from the exhaust port.
Take a look at the "stinger" on the those pipes, they are a lot smaller than the head pipe. There are a lot of other factors involved, such as angles, belly lengths, and convergent cone
angles, as well as stinger diameters and lengths..If you are really interested in this stuff, Look up a fellow by the name of Dr. Gordon Blair of Belfast University.. He is the #1 guy when it comes to 2 cycle technology, and I was fortunate to have a friend that studied under him...I had lots of questions answered, that I couldn't prove that worked, 20 years ago.

JJ,... bigger injectors just mean more fuel....You must have meant bigger throttle bodies....

[ducatiboy]

sounds like you know your stuff.

[Kham]

Originally posted by ducatiboy
sounds like you know your stuff.

you questioning the doctor?